184 THE WATT AND THE TREY1THLCK ENGINES. 



and did not admit so much of the water to the action of the fire 

 as your petitioner's boiler does, and were also in other respects 

 attended with many disadvantages. That your petitioner's inven- 

 tion consists principally in introducing the fire into the midst of 

 the boiler, and in making the boiler of a cylindrical form, which 

 is the form best adapted for sustaining the pressure of high 

 steam. 



" ' That the following very important advantages are derived 

 from this your petitioner's invention. This boiler does not 

 require half of the materials, nor does it occupy half the space 

 required for any other boiler. No mason work is necessary to 

 encircle the boiler. 



" ' That, had it not been for this your petitioner's invention, 

 those late vast improvements which have been made in the use 

 of steam could not have taken place, inasmuch as none of the 

 old boilers could have withstood a pressure of above 6 Ibs. to the 

 inch beyond the atmosphere, much less a pressure of 60 Ibs. to 

 the inch, and is capable of standing a pressure of above 150 Ibs. 

 to the inch.' " 



Trevithick's retrospect views of 1828 are supported 

 by the letter of the late Michael Williams, M.P., the 

 most experienced of Cornish mine workers, but belong- 

 ing to the eastern district that had been for many years 

 the users of the Watt engines in Cornwall. 



" In reference to his great improvements in the steam- 

 engine, I have a more particular recollection, and can con- 

 fidently affirm that he was the first to introduce the high- 

 pressure principle of working, thus establishing a way to the 

 present high state of efficiency of the steam-engine, and forming 

 a new era in the history of steam power. To the use of high- 

 pressure steam, in conjunction with the cylindrical boilers, also 

 invented by Mr. Trevithick, I have no hesitation in saying that 

 the greatly-increased duty of our Cornish pumping engines, 

 since the time of Watt, is mainly owing ; and when it is recol- 

 lected that the working power now attained amounts to double 

 or treble that of the old Boulton and Watt engine, it will be at 

 once seen that it is impossible to overestimate the benefit con- 



